1. Field of the Invention
The present invention relates to a power factor correction (PFC) circuit, and more particularly to a PFC circuit using reverse sawtooth waves and controlling slope of the current.
2. Description of the Related Art
A continuous current mode (CCM) control method is commonly used in conventional PFC circuits. Among the different types of CCM control methods for improving the power factor are a peak current control method, a variable hysteresis control method, and an average current control method. Each of these methods has the advantage of being able to obtain a high power factor.
However, the above different types of CCM control methods have serious drawbacks. That is, in the peak current control method, because of the occurrence of external inductor current distortion and dead angle distortion, and the need to maintain a maximum duty at below 50%, control by precise correction is not possible. Also, with the variable hysteresis control method, when input voltage decreases, there is a significant increase in frequencies to control the inductor current. Therefore, the frequency control is limited according to the input voltage. Finally, in the average current control method, very complicated processes are used in trying to obtain a power factor of 1.00, or unity.